This invention relates to press cylinders in general and more particularly to deflection controlled cylinders.
In deflection controlled cylinders a hollow cylinder is usually braced against the forces, at the roller gap where it is opposite another cylinder, which tend to bend the hollow cylinder, by means of a hydraulic medium which is disposed between the hollow cylinder and a core on the side of the gap between the rollers. In a so-called floating cylinder, a longitudinal chamber which can be filled with pressure liquid is established between the hollow cylinder and the core by means of lengthwise seals arranged at about half-height and corresponding transverse seals provided at the ends of the hollow cylinder. The force exerted on the inner circumference of the hollow cylinder can be controlled by controlling the pressure. The force is constant over the length of the longitudinal chamber. The pressure of the pressurized liquid acts on the other side against the core, which can bend away from the roller gap under the action of this pressure. This deflection is possible because of the space between the hollow cylinder and the core without interfering with the rotation of the hollow cylinder about the core. The forces required in the gap between the rollers are supplied by the deflection of the core without the hollow cylinder itself being bent.
Other design variations of the cylinders under discussion have sliding shoes which bear against the inner circumference of the hollow cylinder and are acted upon by cylinder/piston units provided in or at the core.
The sliding seals of the longitudinal chamber must seal against the inner circumference of the hollow cylinder, which rotates, in part, with very high velocity. While the necessary pressure in the longitudinal chamber can be adjusted without problems, the escape of small amounts of the pressure liquid under the longitudinal seals into a chamber away from the longitudinal chamber, is basically unavoidable. A certain amount of this oil collects in the course of the operation and must be discharged.
The hollow cylinder is supported at its ends on the core, usually by antifriction bearings. These antifriction bearings require lubrication, for which purpose the pressure oil serving as the pressure liquid is used. Overall, a certain amount of oil accumulates at the end of the hollow cylinder, which must be prevented from escaping from the hollow cylinder or must be drained off only through lines provided for that purpose. In order to accomplish this, an annular enclosure terminating cover is provided at the end of the hollow cylinder; it is operatively tightly connected at its outer circumference to the hollow cylinder and at its inner circumference to the core or the stationary roll stand.
The terminating cover often has, in addition, a regular function as a housing, namely, in case where the flection controlled cylinder is driven. The drive shaft is supported in or at the stationary core, goes through the support point of the core in the roll stand and transmits its motion via gearing arranged on the inside of the roll stand to the hollow cylinder. These gears run in oil, of course, and must be enclosed by a kind of housing, which purpose is served in those designs by the "terminating cover," which then is designed more like a housing. Examples for designs of this type are found in DE-OS No. 27 20 219, DE-PS No. 23 07 772 and U.S. Pat. Nos. 3, 290,897; 3,402,679; 3,419,890 and 3,855,681.
At least one of the sealing arrangements provided at the termination cover must be a rotary seal, which permits the relative rotation between the core and the hollow cylinder. Because of the high relative velocities at the sealing point, which can be up to 1,000 m/min, only very high quality seals can be used. These are, in most cases, radially mounted lip seals which consist of plastic material and the lips of which are kept in contact with the counter surface by a coil spring which extends over the circumference and is pre-tightened in tension. While these seals, under ideal conditions, have a good sealing effect and at the same a long service life, these properties are degraded, for instance, if the seal and the counter surface are not exactly coaxial.
This case, however, occurs frequently in the rolls of the type under discussion. This is due to the deflection of the case which takes place in operation. At its end, the hollow cylinder is supported via the antifriction bearings on the core and therefore occupies a definite position relative to the core at the height of the antifriction bearing. The sealing arrangement at the one peripheral rim of the terminating cover cooperating with the hollow cylinder engages at this point. At the other peripheral rim of the terminating cover, however, it cooperates with the core or the roll stand with some spacing in the axial direction. If the core is bent, a dislocation of least one of the sealing arrangements at the two peripheral rims of the terminating cover therefore comes about. While the mentioned lips seals can compensate for small dislocations (which is the very reason for their suitability for such sealing purposes), such seals are not equipped for larger dislocations. It has been found in practice that with large cylinders of the type under discussion, radial dislocations in the order of up to 2 mm at the seal can definitely be expected.
In a floating cylinder, in which the terminating cover is arranged fixed on the core and the lip seal is provided at the outer peripheral rim of the terminating cover, it has already been undertaken to arrange the lip seal in the terminating cover eccentrically to its axis. The eccentricity is chosen so that it corresponds to the deflection of the core expected under the normal operating load of the cylinder, or to the radial dislocation at the height of the seal. Under this definite load, the seal can then run without deformation under ideal conditions. However, as soon as the load changes relative to the value on which the calculated eccentricity is based, the conditions are no longer ideal in this case either.